Test migration parity using existing integration tests

Rakefile

@@ -5,7 +5,7 @@ require 'rake/testtask'
 $LOAD_PATH.unshift(File.expand_path("../lib", __FILE__))
 require "liquid/version"
 
-task(default: [:test, :rubocop])
+task(default: [:test, "test:migrator_integration", :rubocop])
 
 desc('run test suite with default parser')
 Rake::TestTask.new(:base_test) do |t|
@@ -33,6 +33,23 @@ task :rubocop do
   end
 end
 
+namespace :test do
+  task :migrator_integration do
+    ENV['LIQUID_MIGRATOR'] = '1'
+    original_parse_mode = ENV['LIQUID_PARSER_MODE']
+    begin
+      Rake::Task['integration_test'].reenable
+      ["lax", "strict"].each do |parse_mode|
+        ENV['LIQUID_PARSER_MODE'] = parse_mode
+        Rake::Task['integration_test'].invoke
+        Rake::Task['integration_test'].reenable
+      end
+    ensure
+      ENV['LIQUID_PARSER_MODE'] = original_parse_mode
+    end
+  end
+end
+
 desc('runs test suite with both strict and lax parsers')
 task :test do
   ENV['LIQUID_PARSER_MODE'] = 'lax'

test/test_helper.rb

@@ -49,6 +49,27 @@ module Minitest
       assert_equal(expected, output, message)
     end
 
+    if ENV['LIQUID_MIGRATOR']
+      puts "-- Liquid Migrator Enabled"
+
+      alias_method(:assert_template_result_without_migrator, :assert_template_result)
+
+      def assert_template_result(expected, source, assigns = {}, error_mode: nil, partials: nil, **kwargs)
+        migrated_source = Liquid::Template.migrate(source, line_numbers: true, error_mode: error_mode&.to_sym)
+        assert_no_migration(migrated_source)
+        if partials
+          migrated_partials = {}
+          partials.each do |name, partial|
+            new_partial = Liquid::Template.migrate(partial, line_numbers: true, error_mode: error_mode&.to_sym)
+            assert_no_migration(new_partial)
+            migrated_partials[name] = new_partial
+          end
+        end
+        assert_template_result_without_migrator(expected, migrated_source, assigns,
+          error_mode: 'strict', partials: migrated_partials, **kwargs)
+      end
+    end
+
     def assert_match_syntax_error(match, template, error_mode: nil)
       exception = assert_raises(Liquid::SyntaxError) do
         Template.parse(template, line_numbers: true, error_mode: error_mode&.to_sym).render
@@ -60,6 +81,10 @@ module Minitest
       assert_match_syntax_error("", template, error_mode: error_mode)
     end
 
+    def assert_no_migration(source)
+      assert_equal(source, Liquid::Template.migrate(source))
+    end
+
     def assert_usage_increment(name, times: 1)
       old_method = Liquid::Usage.method(:increment)
       calls = 0

test/unit/migrate_unit_test.rb

@@ -107,10 +107,6 @@ class MigrateUnitTest < Minitest::Test
 
   private
 
-  def assert_no_migration(source)
-    assert_equal(source, Liquid::Template.migrate(source))
-  end
-
   def assert_migration(source_to_expected_output_hash)
     source_to_expected_output_hash.each do |source, expect|
       message = "source: #{source.inspect}"